The present invention relates generally to input buffers of the type commonly employed in semiconductor devices, and, more particularly, to an input buffer having a compensation circuit for stabilizing the output thereof.
With reference to FIG. 1, there can be seen an input buffer of conventional construction. The conventional input buffer depicted in FIG. 1 includes a PMOS transistor 1 whose source electrode is connected to the supply voltage Vcc and whose gate electrode is connected to an enable signal EN; a PMOS transistor 2 whose gate electrode is connected to the source electrode of PMOS transistor 1 and whose gate electrode is connected to an input signal IN; an NMOS transistor 3 whose drain electrode is connected to the drain electrode of PMOS transistor 2, whose gate electrode is connected to input signal IN, and whose source electrode is grounded; and, an NMOS transistor 4 whose drain electrode is connected to the drain electrode of NMOS transistor 3, whose source electrode is grounded, and whose gate electrode is connected to the enable signal EN.
In operation, when the enable signal EN goes "high", NMOS transistor 4 is turned on, thereby driving output signal (OUT) "low", regardless of the logic level of the input signal (IN). When the enable signal EN goes "low", NMOS transistor 4 is turned off and PMOS transistor 1 is turned on, thereby pulling up the voltage level of the source electrode of PMOS transistor 2 to near Vcc. At this time, if the input signal (IN) is "high", the output signal (OUT) is "low", and conversely, if the input signal (IN) is "low", the output signal (OUT) is "high". When the enable signal EN and the input signal IN are low, fluctuations of the supply voltage Vcc cause corresponding fluctuations of the output signal OUT, which constitutes a significant drawback.
Based on the above, it can be appreciated that there presently exists a need in the art for an input buffer which does not suffer from the above-described drawback of the presently available input buffers commonly utilized in semiconductor devices. The present invention fulfills this need.